Tell your mam! thats first thing... no matter what has went on before mams know best, and theyre alot more understanding than we give them credit for when were younger.
book a doctors appointment to find out exactly how far along you are, and sort out the next steps
In reality you need to think about the options. If you keep it will the father support you? will you finish school? go to college? where will you live etc?
If not would you put it up for adoption or get rid of it. Bearing in mind both sides of the arguments- ie how hard it is to give up a baby, and how hard it is to have one at a young age.
Once you know better how you feel then talk to the father
but the main thing is to stay calm. Its never as bad as it seems, and you will always manage no matter what happens. keep your chin up. x